In SQL, comparing values is fundamental to data retrieval and manipulation. One of the most common comparisons is checking if two values are not equal. This is achieved using the 'not equal to' operator. The `!=` operator is the most common way to express this in many SQL dialects, including MySQL, PostgreSQL, and SQL Server. Alternatively, `<>` is also used in some databases. These operators are essential for filtering data based on specific criteria, such as finding all customers who haven't placed an order or identifying products with prices different from a certain threshold. Understanding how to use these operators effectively is crucial for writing efficient and accurate queries. The choice between `!=` and `<>` is largely a matter of personal preference or database convention. However, it's important to be consistent within a project to avoid confusion.